Depression is associated with high rates of relapse and recurrence during a patient's lifetime. Current guidelines regarding treatment recommend 4 to 9 months of continuation antidepressant therapy following remission of acute symptoms to allow more complete resolution of the episode. In this article, we test whether adherence to these recommendations reduces the likelihood of relapse or recurrence in a Medicaid population. Methods: We used a Medicaid database covering 1989 through 1994. The

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... ple consists of the 4052 adult patients who filled an antidepressant prescription at the time of an initial diagnosis of depression. These patients were followed up for up to 2 years. Timing and counts of antidepressant prescription claims are used to construct a proxy measure for adherence to guidelines. Relapse or recurrence is defined by evidence of a new episode requiring antidepressant treatment, hospital admission for depression, electroconvulsive therapy, emergency de-partment visit for mental health, or attempted suicide. We used survival analysis to predict relapse or recurrence for each patient and to examine the effect of following treatment guidelines on relapse and recurrence. Results: Approximately one fourth of the patients had a relapse or recurrence during their follow-up period. Factors that affect relapse and recurrence include comorbidities, race, and guideline adherence. Those who continued therapy with their initial antidepressant were least likely to experience relapse or recurrence; those who discontinued their antidepressant early were most likely to experience relapse or recurrence. Conclusion: Adherence to depression treatment guidelines with an antidepressant that is likely to have continuous use by patients reduces the probability of relapse or recurrence.